I have a 78 corvette, automatic, and the other day when i returned the car to the garage and turned the car off I noticed it was running a little hot, not overheating, just hotter than usual. I turned off the car and heard a boiling/bubbling noise, like coffee perculating. I checked and there was a puddle of antifreeze on the ground of the garage. I refilled the resevoir and started the car again letting it run for 15 mins to get the antifreeze through the engine. I looked under the car and noticed it was dripping to the ground. I could not see where it was coming from but the resevoir was empty. I have heard that the bubbling sound might be from air in the line and might be resolved with replacing the radiator cap and thermostat. What are your thoughts?
Replacing the radiator cap is a cheap way to rule it out as the cause, but I think something else is going on. I think you need to have your cooling system pressure-tested. The radiator might also need to be flow-tested.
This coolant boiling problem can be caused by a busted cooling fan, clogged passages in the radiator, a closed thermostat, etc.
I start with a close examination and a pressure test to find the leak.
I’d do a pressure leakdown test of the cylinders also.
If you have a blown headgasket the hot combustion gasses will be being blown into the water jacket with every cylinder firing. That’ll heat the coolant up beyond its ability to dissipate heat, reduce the cooling system’s ability to disspate heat (water transfers heat far better than the gasses) and the gasses will displace and push the coolant out into the reservoir…and onto the ground through the reservoir overflow tube.
By the way, by filling the reservoir and letting the engine run you were not getting coolant into the engine. The only way it gets there from the reservoir is when the engine cools and contracts, drawing fluid back into it through the radiator cap.
the time of peak coolant heat, is when you turn the engine off. This is because the engine is as hot as it was when you were driving, but the coolant is no longer circulating through the radiator, and the fan is not running. Many owners of older cars such as yours install electric cooling fans that come on for several minutes after the engine is shut down to compensate for this rise in coolant temp. When coolant is hot is expands, and the relief valve in the radiator cap allows it to flow out of the radiator into the overflow tank. This can make a bubbling noise. Once the engine and coolant cool down, the coolant contracts and this will suck the coolant back into the radiator. but if there is a crack in the overflow tank, or the hose to it, you will get coolant on the floor. This is not to rule out something more serious, certainly if this condition is new to your car and you have had it a long time, then follow all the previous advice to avoid major damage to your lovely old car.
“Many owners of older cars such as yours install electric cooling fans that come on for several minutes after the engine is shut down to compensate for this rise in coolant temp.”
Have your cooling system pressure tested for leaks…That puddle on the floor came from SOMEPLACE…
If no leaks are found, and this continues, your engine might have a “hot’spot”, a place in the head(s) where corrosion has restricted coolant flow…